RATE OF MOVEMENT OF THE BLOOD 



207 



shape of the letter U (Fig. 62), or by merely allowing the vessel to 

 bleed into a graduated tube and seeing how long the blood column takes 

 to travel from one end to the other. This method is of considerable 

 value in measuring the velocity of flow from small vessels such as the 

 veins coming from glands and muscles. For larger vessels a so-called 

 stromuhr is employed. There are numerous forms of stromuhr; that 

 shown in the diagram (Ludwig's) (Fig. 62) consists of two glass bulbs 

 united above, and connected below with tubes that open flush with the 

 surface of a brass disc. This is pivoted at its center with another similar 

 platform also having flush with the surface the openings of two tubes con- 

 nected with the cut ends of the artery or vein. In a certain position of 

 the platform, the tubes from the artery or vein are exactly opposite 

 those of the bulbs, so that the blood can flow from one end of the vessel 



Fig. 62. Forms of apparatus for measurement of blood velocities. 



i. Volkmann's hemodromometer. The blood vessel is attached to the two short side tubes, 

 and according to the position of the stopcock, the blood flows either directly between them or 

 through the U-shaped glass tube. 



z. I/udwig's stromuhr. The tubes on the lower end of each of the two glass bulbs pierce 

 a circular brass platform and end flush with its surface. This platform pivots at its center on 

 a similar lower platform with two openings connected with the tubes that lead to the blood 

 vessel. 



through the bulbs to the other end. To use the instrument the proxi- 

 mal bulb is filled with oil and the peripheral one with physiologic saline. 

 The clip is then removed from the central end of the artery, and the blood 

 flows in and displaces the oil, which in turn displaces the saline in the 

 peripheral end of the artery. When the blood has risen to a mark on 

 the tube joining the two bulbs, the instrument is rapidly rotated so that 

 the oil is brought back again into the proximal position, the rotation 

 being effected so quickly that there is no distinct interruption in blood- 

 flow. The operation is repeated in this way for a given period of time. 

 Counting accurately the number of revolutions, then multiplying the 

 number of revolutions by the capacity of the bulbs, we get in cubic 



